Reports surfaced last week that Twitter was talking to Dorsey about a possible return.

Twitter CEO Dick Costolo announced – yes, also in a tweet – that he was excited that Dorsey is “returning to the company day-to-day leading product as Executive Chairman.”

There was no immediate word on the status of co-founder Evan Williams, who Costolo replaced as CEO in October. At the time, Williams said he was wanted to be “completely focused on product strategy,” although reports have since surfaced that Williams rarely appears at Twitter headquarters.

Dorsey was ousted as CEO by Williams in 2008.

In a written statement,Twitter downplayed any discord between the three co-founders, saying Williams, Dorsey and Biz Stone “have unselfishly played whatever role was most needed at the time to nurture the company and help the product reach its full potential. Jack has been involved with the company from day one in various roles.”

“As executive chairman, Jack will dive in to work with more than 450 people, led by an experienced executive team. The timing is fortuitous; not only is Twitter experiencing record growth, but we also now have a new infrastructure that will keep us ahead of that growth and enable us to launch products that will make Twitter more instant, simple and always present.”